A self-assembled monolayer is referred to one that adsorb or chemically bind to a surface of a solid substrate and form a monomolecular layer (film) exhibiting high orientation due to interaction between the molecules. Incidentally, the self-assembled monolayer is also referred to as a self-organized monolayer or a self-integrated monolayer, but it is referred to as a self-assembled monolayer or simply a SAM film in the present specification.
The SAM film has been rapidly developed since it was reported that the SAM film formed on a glass substrate by using organosilane compounds (see Non-Patent Document 1) and also on a gold substrate by using organic sulfur compounds (see Non-Patent Document 2).
The SAM film is more stable than the LB (Langmuir-Blodgett) film and can be formed by a gas phase reaction, and its application range has been widened. In addition, the thickness of the SAM film is determined by the size (length) of the molecule and the angle of inclination thereof to the substrate, and it is possible to produce precisely and conveniently a film in a molecular level of about 1 nm. Generally, about 0.2 nm of a film thickness correspond to one methylene unit in an alkyl chain, and it is possible to produce accurately a monolayer having a desired film thickness by adjusting the length of the alkyl chain.
It is possible to modify the properties of the surface of a solid substrate by forming a SAM film. For example, in an organic field effect transistor (organic FET) in which silicon oxide is generally used as an insulating layer, it has been reported that a SAM film of organic silane compounds such as octadecyltrichlorosilane (OTS) formed on the silicon oxide imparts water repellency to the surface of the insulating layer. As a result, the adjacent (organic) semiconductor improves in crystallinity, and therefore the charge mobility thereof is increased. Accordingly, it is possible to control the hydrophilicity or hydrophobicity of a surface of a solid substrate by forming a SAM film on the surface of the solid substrate.
In addition, it is possible to impart a specific function to a surface of a solid substrate by introducing a functional group exhibiting functionality to moiety of molecules forming a SAM film. For example, it is possible to impart various functions such as electron transfer and oxidation-reduction reactions, catalysis, light-induced electron transfer, electrochemical luminescence, recognition of ions and molecules, biosensor, bio-molecular devices, and photovoltaic power generation and the like to a surface of a solid substrate by forming a SAM film. The application of a SAM film in these fields is expected.
For example, it has been reported that formation of a SAM film using alkylenethiol compounds which have an amino group as an end group to anchor a saccharide having an aldehyde moiety or a compound having a carboxyl group (see Patent Document 1), formation of a SAM film using alkylenethiol compounds which have an electron accepting functional group such as a cyano aryl group at an end group (see Patent Document 2), formation of a SAM film exhibiting ultraviolet resistance using alkylenethiol compounds which have a polyphenylene group at an end group (see Patent Document 3), formation of a SAM film having a rigid adamantane surface film structure using bis(adamantylmethyl)disulfide (see Patent Document 4), formation of a SAM film for lithography using compounds having an alkylene chain in the middle of which a functional group sensitive to a relatively long-wavelength light is introduced so that the film is able to be patterned with the light (see Patent Document 5), formation of a SAM film for a photovoltaic cell or a photocharge separating element using compounds obtained by binding a pyrrole ring-expanded porphyrin and a fullerene covalently (see Patent Document 6), and the like.
Meanwhile, a report that a SAM film is formed using triptycene derivatives is not found. However, there are reports about triptycene derivatives as follows, an organic EL material made from polymers or copolymers of triptycene (see Patent Document 7), a method for producing triptycenediamine which is a raw material for a polyimide resin and a polyamide resin (see Patent Document 8), a liquid crystal polymer composition using a compound that is generically called “iptycenes” obtained by linking between triptycenes (see Patent Document 9), a polyamide acid obtained by reacting triptycenetriamines, a polyimide resin obtained by heating the polyamide acid, and an optical part using the resin (see Patent Document 10), use of a triptycene ring as a component of a macrocyclic module which is a material for a nanofilm (see Patent Document 11), a method for optical resolution of triptycene derivatives using enzyme (see Patent Document 12), an insulating film and an electronic device containing polymers which are obtained by polymerizing triptycene derivatives having a plurality of triple bonds or double bonds as a polymerization unit (see Patent Document 13), triptycene derivatives for photoresist having at least one acid-dissociable dissolution-inhibiting group (see Patent Document 14), and a liquid crystal polymer composition using compounds which have triptycene-1,4-diyl groups (see Patent Document 15), and the like.
In addition, it has also been reported that triptycene derivatives substituted with 1, 2, 5, or 6 long-chain alkoxy groups are regularly aligned to form smectic liquid crystals (see Non-Patent Document 3), but it is not disclosed that three substituents are regularly aligned in the same direction and the triptycene derivatives are suitable as a SAM film-forming material.
The present inventors have found out that triptycene derivatives (Janus-type triptycene derivatives) in which three identical substituents regularly align in the same direction form a film as substituents of the derivatives align in the same direction and integrate. Furthermore, they have reported that the film formed in this manner is self-assembled and further treatment provide a self-assembled monolayer (see Patent Document 16).